Hair Follicle Response to the Variable l.e.t. of a Helium Ion Beam B.M. De Rey A1, O.A. Bernaola A1, R. Mazzei A1, G. Suquet A1 A1 Radiobiology Department, National Atomic Energy Commission Avda. del Libertador 8250, Buenos Aires, Argentina Abstract: A homogeneous population of hair follicles in the rat tail has been used to analyse the in vivo response of a biological system to heavy particle irradiation. The conical configuration of the rat tail gives rise to a variable energy degradation of the beam thus yielding information on the damage elicited by the increasing l.e.t. of the helium beam at different sites on the same sample. By means of scanning electron microscopy three different zones were observed as direct evidence of helium ion penetration in the tail. Quantitative evaluation of radiation damage yielded results concerning hair follicle damage after increasing doses for different regions of the ionization curve. Keywords: Helium Ions, Hair Follicles, Bragg-peak